1. Field of the Invention
The present invention relates to a junction substrate composed of a plurality of substrates and a method of bonding the substrates together.
2. Description of the Related Art
In recent years, small-sized reactors called microreactors have been developed. The microreactor is a small-sized reactor in which a plurality of reactants such as materials and reagents are allowed to react with each other while being mixed together. The microreactor is utilized to carry out chemical reaction experiments in micro areas, develop drugs, or develop artificial organs or is utilized as a genome and DNA analysis tool or a basic analysis tool for microfluid engineering. Chemical reactions using the microreactor have characteristics not exhibited by normal chemical reactions using beakers or flasks. For example, the microreactor is advantageous in that the whole reactor is so small as to provide a very high effectiveness of regenerator to allow efficient temperature control required for reactions. Thus, the microreactor makes it possible to quickly and easily accomplish reactions requiring precise temperature control or rapid heating or cooling.
Specifically, the microreactor is formed with, for example, a channel through which reactants flow and a reactor in which reactants react with each other. In Jpn. Pat. Appln. KOKAI Publication No. 2001-228159, a silicon substrate in which a groove with a predetermined pattern is formed is anodically bonded to a Pyrex™ substrate so that they are laminated to each other. A channel is then formed in a closed area between the two substrates. The “anodic bonding” is a bonding technique to apply a high voltage to substrates in a high-temperature environment to generate an electrostatic attraction between the substrates, thus chemically binding the two substrates together at an interface. The anodic bonding is particularly excellent among substrate bonding techniques because the substrates can be strongly bonded together without using any coating agent and in the atmosphere.
Some microreactors are provided with heating means for heating a channel in order to facilitate reactions in the reactor. For example, it is contemplated that to transfer heat to a channel portion via a substrate, a heating resistant film corresponding to the channel pattern and an interconnect made of metal to supply power to the heating resistant film may be formed on a side of a front surface of a glass substrate or the like (the surface of the substrate which is opposite the surface bonded to a silicon substrate). In this case, when the glass substrate and the silicon substrate are anodically bonded together via the heating resistant film and interconnect, electric fields concentrate in parts of the front surface of the glass substrate which are close to the heating resistant film and interconnect. Consequently, Na from the glass substrate is locally precipitated in these parts. As a result, Na may enter the heating resistant film and/or the interconnect, deposited on the heating resistant film in order to apply a voltage to the heating resistant film. These impurities may create fine gaps in the heating resistant film, interconnect film and/or its front surface to make it rough. Consequently, the heating resistant film and/or the interconnect film may be peeled off from the glass substrate or a metal electrode may be peeled off from the heating resistant film.
The present invention is advantageous in that when a glass substrate or the like which contains Na is anodically bonded to another substrate, Na from the substrate is hindered from being locally precipitated.